Shutters for windows and doors usually have a frame, hinged to the window or door opening, and rotatable louvres extending across the frame, from side to side. The louvres are elongated blades, some with aerofoil shapes, and having pivots at each end along their central axis. A control typically a control bar is connected to the louvres. Moving the control bar rotates all the louvres. In this way the louvres can be tilted open for light and air, or tilted up or down and closed for privacy and to exclude light. Shutters have been made in this general pattern for hundreds of years.
In the past, shutters were usually made of wood. The control bar was connected to the louvres, in earlier designs, by a pair of wire staples, one secured to the control bar and the other secured to the louvre. More advanced systems have been developed, and such shutters now are commonly made of synthetic plastic materials, although wood is still preferred by some consumers.
Louvres must be fitted to window or door openings of a particular building.
The dimensions of these window or door openings may and usually do vary from one building to another, and from one room to another in a given building.
The first step is to measure the width and height of the opening.
The shutters must then be designed and made to fit those measurements.
The shutter frame is usually a rectangle with vertical side members and horizontal top and bottom members. The louvres must of course be of a length to fit from one side member to the other.
However, determining the number of louvres to be fitted into a shutter frame of a specific custom fitted measurement is more difficult. If there are too many louvres then when they are open there will not be sufficient space between them.
If there are too few louvres then they may not close completely at the top and bottom of the frame. Some degree of overlap or contact is required when the louvres are closed, to provide effective exclusion of light, and for privacy.
When tilted closed it is desirable that the louvres should close as tightly as possible. The purpose is to exclude light or at least to shade the interior from sun light as far as possible, and also of course to provide some privacy.
The louvres must therefor overlap when closed. At the top and bottom of the frame there is often no overlap. The top and bottom louvres simply tilt with their edges as close as possible to the top and bottom of the frame. In many cases there was a gap, and light was still admitted.
To satisfy these problems the manufacturer of the shutters sometimes built shutters with custom specific spacings between the pivot centres of the louvres. This would result in more or less overlap between louvres depending on the spacings between their pivot centres, but the variation should not be excessive, from one shutter to another, since this will change their aesthetic appeal.
In other cases, the manufacturer would use top or bottom frame members of different widths. This would simply take up any space left uncovered by the louvres.
However, this required the manufacturer to keep various different pieces of material, to provide frame members of the required width.
It might be thought that the louvres could be made in various widths, to answer this problem. This is not really practical. The louvres are usually of a predetermined width, for reasons of economy, and so as to avoid too many variables in manufacture.
The top and bottom louvres must still tilt as close as possible to the top and bottom of the frame, as explained above.
Even when great care is taken to ensure a close fit, it is inevitable that there will be some light admitted between the top and bottom louvres and the top and bottom of the frame, since here there is no overlap.
One approach towards this problem is shown in U.S. Pat. No. 6,810,620, R. Anderson Nov. 2, 2004.
In this system, there were adjustable frame extensions at the top and bottom of the frame. The extensions could be positioned at various degrees of extension from the frame, during manufacture.
Their purpose was to allow greater flexibility in the building of the shutter, and to enable what was essentially the adjustment of the width of the top and bottom frame members thereby enabling the fitting of a given number of louvres in frame, thereby allowing some variation in the height dimension of the frame.
By simply positioning the frame extensions at a greater or lesser distance, the top and bottom members of the frame could in effect be made taller or shorter.
However, this was not totally satisfactory. Adjusting the height dimension of the top and bottom frame members, in this way, would also change the way the louvres closed. The geometry of the whole shutter would be affected by extending or retracting the extensions. When the extensions were extended too far then the extension would contact the top and bottom louvres, before the rest of the louvres in that shutter had fully closed.
When the extensions were not extended a sufficient distance there would be no actual contact between the top and bottom louvres and the extensions, because the rest of the louvres in that shutter had already fully closed.
It is desirable to provide a shutter with a frame and louvres and a control bar and having louvre seals at the top and bottom of the frame, which are flexible and swingable both ways to provide for an overlap between the top and bottom louvres and the seals, and to provide good contact between the top and bottom louvres and the seals for the exclusion of light, when the shutter is closed.